THE NECTURUS 19 



Muscles are usually associated together in pairs or oppos- 

 ing groups. Some of the names that appear are depressor - 

 levator, tensor - flexor, pronator - supinator, adductor - 

 abductor, sphincter - dilator. 



The division of muscles into voluntary and involuntary 

 is a very necessary development since internal parts must 

 function with little or no attention from the individual. 

 Involuntary muscles are found in the intestines, heart, 

 and in other places where such a type is desirable. In- 

 voluntary muscles are unstriated except in the heart. 

 Voluntary or striated muscles are attached to movable parts 

 that must make more rapid movements. 



The muscle insertion may be of several types according 

 to the mechanical needs. Broad muscular attachments are 

 found in regions where this type is most effective mechanic- 

 ally. In parts where space is limited, or bulk would be 

 undesirable the muscles end in tendons. In the wrists 

 and ankles for example, long tendons connect muscles 

 with their attachments, thus reducing the size and making 

 the part more flexible. 



Since the parts of the body wear out, many adaptations 

 will be found in the muscular and skeletal systems for 

 preventing friction. Where muscles rub together they are 

 protected by membranes. Where they pull over bone, 

 pulley like arrangements are developed. In advantageous 

 spots sesamoid or tendon bones are developed, such as the 

 patella of the knee. These greatly lessen the possibility 

 of over wear. Good examples of tendon bones may be 

 seen in the legs of chickens and turkeys. 



For convenience in consulting, a list of the muscles of 

 various regions is given at this point. 



Muscles of the Head and Throat 



Masseter 

 Temporalis 



